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. 2013 May;54(3):515-31.
doi: 10.1093/jrr/rrs124. Epub 2013 Feb 5.

Facility optimization to improve activation rate distributions during IVNAA

Atiyeh Ebrahimi Khankook  1 , Laleh Rafat Motavalli, Hashem Miri Hakimabad
Affiliations

Facility optimization to improve activation rate distributions during IVNAA

Atiyeh Ebrahimi Khankook et al. J Radiat Res. 2013 May.

Abstract

Currently, determination of body composition is the most useful method for distinguishing between certain diseases. The prompt-gamma in vivo neutron activation analysis (IVNAA) facility for non-destructive elemental analysis of the human body is the gold standard method for this type of analysis. In order to obtain accurate measurements using the IVNAA system, the activation probability in the body must be uniform. This can be difficult to achieve, as body shape and body composition affect the rate of activation. The aim of this study was to determine the optimum pre-moderator, in terms of material for attaining uniform activation probability with a CV value of about 10% and changing the collimator role to increase activation rate within the body. Such uniformity was obtained with a high thickness of paraffin pre-moderator, however, because of increasing secondary photon flux received by the detectors it was not an appropriate choice. Our final calculations indicated that using two paraffin slabs with a thickness of 3 cm as a pre-moderator, in the presence of 2 cm Bi on the collimator, achieves a satisfactory distribution of activation rate in the body.

Keywords: IVNAA; MCNP; activation rate; collimator; neutron flux uniformity; pre-moderator.

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Figures

Fig. 1.
Fig. 1.
Schematic view of the irradiation facility: (A) 3D-dimensional view; (B) a cross-sectional view. Only one pair of detectors and sources can be seen in this view.
Fig. 2.
Fig. 2.
Macroscopic cross-section of neutron interactions with some compounds used in this paper: (A) absorption; (B) elastic scattering; (C) total; (D) (n,2n).
Fig. 3.
Fig. 3.
Neutron quality factors versus energy, which were previously reported in NCRP 38.
Fig. 4.
Fig. 4.
Detector spectrum using different PMs with similar thicknesses (1.0 cm).
Fig. 5.
Fig. 5.
Detector spectrum using different collimators with the same PM (1.0 cm paraffin).
Fig. 6.
Fig. 6.
Activation rate and thermal neutron flux volume histograms of some important organs.
Fig. 7.
Fig. 7.
2D plot of the activation rate (A), thermal neutron flux (B), fast neutron flux (C) and energy deposition (D) in a two-dimensional array at mid-depth of the phantom (Y = 0). A YZ-plot of energy deposition (E) located in X = –3 cm is also presented.
Fig. 8.
Fig. 8.
Prompt gamma neutron activation cross-section in terms of photon energy of Al.
See this image and copyright information in PMC

References

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